State Senator Kevin de León shakes hands with supporters during an event held to formally announce his run for U.S. Senate on October 18, 2017, in Los Angeles.

Last Thursday, the more than 500 delegates to the convention of the California Labor Federation—the state’s AFL-CIO—voted to endorse liberal Democratic State Senator Kevin de León’s insurgent and uphill bid to unseat longtime incumbent Senator Dianne Feinstein, whom the federation had supported in all her previous U.S. Senate elections, dating back to 1992. Coming from a pillar of the state’s Democratic establishment, the endorsement—which required a two-thirds vote of the delegates—was a stunning development.

The following day, the leaders of New York’s progressive unions announced that they were severing ties with the state’s Working Families Party—an organization that many of those unions had founded and supported, and that has backed, with notable success, a range of pro-labor progressive candidates in Democratic primaries over the past two decades. The announcements came on the eve of the party’s Saturday meeting, at which it was expected to endorse liberal Cynthia Nixon’s insurgent and uphill Democratic primary challenge to Governor Andrew Cuomo (which, in fact, it did). As reported in The New York Times, the governor had made clear to the unions—most of which had already endorsed him—that they also had to sever their ties to organizations that backed Nixon’s candidacy.

“If unions or anyone give money to any of these groups,” Cuomo said in a meeting earlier in the week attended by WFP State Director Bill Lipton, who recounted Cuomo’s statement to the Times, “they can lose my number.”

“These groups” included not just the WFP but also Make the Road Action, which is the political arm of the state’s largest immigrant rights group; New York Communities for Change, the successor group to New York ACORN and the foremost political organizer in the state’s black communities; and Citizen Action, the leading progressive activist group upstate. The three groups also play an active role in the WFP, and their delegates to the WFP’s Saturday convention were largely among those who voted to endorse Nixon. Until Friday, most of the state’s progressive unions played an active role in the WFP, too, and provided it—and those other three groups—with much of their funding. Two of those unions—Local 32BJ of the Service Employees International Union, which represents many thousand of New York’s building service workers, and the Communications Workers, which was one of the three groups that effectively founded the WFP—announced their departure from the party.

Like their West Coast counterparts’ endorsement of de León, the New York unions’ split with the WFP was a stunning development, too.

The de León and Nixon challenges to Feinstein and Cuomo have a good deal in common. Both candidates are attacking their opponents from the left—de León building on his record as state senate president, where he steered into law the state’s $15 minimum wage, its “sanctuary state” statute, and landmark environmental legislation; Nixon coming to the campaign not just as a celebrity advocate for progressive causes but also as a leader in the movement to defend and improve the state’s public schools.

De León criticizes Feinstein for her periodic—but cataclysmic—adhering to center-right positions, whether it be her vote to authorize the Iraq War, her support for George W. Bush’s regressive tax cuts, or her more recent willingness to cut President Trump more slack than any other non-Republican Californian elected official has. De León, who also got a single-payer bill through his state senate, is running as the tribune for today’s California—by the indices of election results and state policy, the leftmost state in the union—while casting Feinstein, plausibly, as the tribune of the whiter, more centrist state that elected her 26 years ago.

Nixon—like de León, a single-payer advocate—criticizes Cuomo for going back on his 2014 pledge to help Democrats retake the state senate (lest it reflect the state’s liberalism)—a pledge he made to the WFP as a condition of winning its endorsement that year. Nixon has attacked Cuomo for his dismissal of the commission investigating Albany corruption, and what even his supporters admit is his thuggish way of doing business. She is running as the policy wonk outsider who has none of Cuomo’s circle-the-wagons instincts when it comes to cleaning up Albany, and a leader who could infuse New York’s politics with more small-d democracy by making it easier to vote in the state’s primaries.

So—two very similar candidates, both in substance (progressive) and prospects (daunting but not impossible). Similar, too, in being the most prominent challenges that the newly energized left of the Democratic Party is directing at its old-guard center.

So—why the diametrically opposed responses from the labor movements of the two states with the greatest number of union members? Among the unions that have either themselves endorsed de León or voted last Thursday for the AFL-CIO to endorse him were many of the same ones that pulled back from the WFP for its Nixon heresy last Friday, SEIU and the CWA among them.

First, let’s look at what the unions in the two states have in common. The New York unions that were part of the WFP can hardly be said to have warm feelings for Cuomo: His years effectively defending Republican rule in the state senate and his support for the charter school movement, to cite just two particulars, have infuriated many of the unions that felt compelled to endorse him.

Similarly, the California unions have never viewed Feinstein as a leader in labor or liberal causes. “When we endorsed her six years ago,” says one leading California union leader, “it was with a sigh. It was begrudging. She touts her seniority, but she hasn’t used her seniority to promote progressive issues. She’s increasingly distanced from California, not just geographically but politically. She doesn’t know us or what our concerns are.” (Indeed, Feinstein didn’t attend the federation convention, and in the letter she sent in her stead, she wrote, “I regret that I don’t know as many of you as I would like. … Please call my office, I would be very happy to meet with you.”)

By contrast, said Art Pulaski, the Labor Federation’s executive secretary-treasurer, de León was known not just to the labor delegates in the hall but to many, and perhaps even most, of the state’s liberal activists. “He reflects where California is right now, in its clear support for immigrants, in expanding social insurance and workers’ rights.”

So again—why the difference between West Coast and East Coast labor? Partly, it’s due to each state’s peculiar electoral laws.

In California, the law of the jungle primary dictates that only the top two finishers in June’s primary, regardless of party, move on to the November general election. Given the continuing decline of state Republicans (there have been more than 70 contests for statewide offices since Republican Governor Arnold Schwarzenegger won re-election in 2006; Democrats have won all of them), it’s a certainty that Feinstein and de León will finish one-two and move on to the November run-off. Filing has already closed and no prominent Republican is running for Senate (no write-ins are allowed in November, either). It would be overstating it to call the Republicans who are running merely obscure; more precisely, they’re completely unknown, with no visible means of campaign financial support.

So whomever labor endorsed, they could be sure that a Democrat would win. The worst thing that could happen would be a Feinstein victory. (For that reason, de León will probably have to narrow Feinstein’s lead to about a dozen percentage points in the June primary for the unions to judge him a credible November challenger. Only then, given the unions other election-year commitments, would they be likely to start seriously funding his campaign.)

In New York, the state’s unique electoral fusion law enables candidates to run as the nominee of more than one party—so that Nixon, were she to win the Democratic primary in September, could run on both the Democratic and Working Families ballot lines. That leaves open the possibility that in November, she could split the vote with Cuomo—she as the WFP candidate if she fails to win the Democratic primary, he as the Democratic candidate if he does—and thereby allow a Republican to win the election.

Indeed, this was the argument that some of the unions made as they went through the motions of asking the WFP not to endorse Nixon. “We are deeply, deeply concerned about creating a spoiling situation,” Beverly Brakeman of the United Auto Workers Region 9-A—one of the WFP’s leading supporters—said in opposing the party’s Nixon endorsement.

But the odds that Nixon would somehow enable a Republican to win the governorship are slim. In the many hundreds of elections in which the WFP has fielded candidates, it almost never has backed a candidate other than the Democrat in a general election where a Republican had even the remotest chance of winning. In answering questions from the WFP’s executive committee, Nixon pointedly declined to pledge she’d soldier on if she lost the Democratic primary and Cuomo had a serious Republican challenger (which as yet, he does not). I suspect Nixon and the WFP would likely decide not to challenge Cuomo were that the case—and most of the union leaders know that.

What made the difference between labor’s left coast and its right, then, really comes down to a difference in character: Feinstein’s and Cuomo’s. California labor may not be entranced by Feinstein, but neither they nor anyone else fear her. Cuomo, by contrast, governs by fear. As his war on New York’s Mayor Bill de Blasio and his betrayal and harassment of the WFP make clear, he seeks to stamp out any rival or potential rival, even when he could turn them into occasional allies. That made all too credible his threats to cast the unions that already support him out into the cold unless they cut off their support for groups that backed Nixon in the Democratic primary—never mind that those were the groups that spearheaded the successful campaign to raise New York’s minimum wage to $15 and are heading the ongoing efforts to protect the city’s immigrant communities from Trump’s agents.

To be sure, like most Democratic electeds, Cuomo has noticed the rising liberalism of the Democratic base, and has responded with some notable initiatives—like the $15 wage. But fear outweighed appreciation in labor’s calculations—and if it didn’t, Cuomo’s threats surely tipped the balance. The unions can’t risk antagonizing a governor whose vindictiveness could descend upon their members, and the WFP—which has declined to criticize any of the unions that have pulled up stakes in recent days—understands that very well.

In the comic film The Death of Stalin now playing in theaters, members of the Soviet politburo stand by in paralyzed inaction as Stalin lies sprawled on the floor beside them, unconscious from a stroke. He has recently declared doctors to be enemies of the state, so best not to call them, but best to stay there to demonstrate, however ineffectually, their continued loyalty.

I’m not equating New York’s union leaders to the politburo, of course, and I’m not equating Cuomo to Stalin, at least when it comes to the substance of their policies and their methods of enforcing them. But the paranoia and vindictiveness of the man on the Kremlin floor and the man in Albany’s governor’s mansion have inspired fear and insecurity not just among their critics but among their supporters as well.